Without limiting the scope of the invention, its background is described in connection with optical interconnects. Heretofore, in this field, it has been shown that optical interconnects are more efficient in terms of power and speed for connection lengths longer than a break-even distance Optical interconnections can be divided into two categories, guided wave and free-space optics. Guided wave interconnection uses optical fiber or integrated optics methods. Disadvantages of guided wave optical interconnects include fixed interconnects and a crowded backplane. The advantage of guided wave connection is the precision in reaching the destination. However, free-space optics can provide similar advantage if properly arranged. Furthermore, free-space optics solve routing restriction by utilizing the advantage of noninteractive property of photons when crossing over.
Many free-space optical interconnection methods have been proposed, such as computer generated hologram (CGH), and crossbar switch with spatial light modulators (SLMs). A CGH can be used in volume interconnection but in a fixed connection pattern and associated with a lower light efficiency because all optical paths should exist at all times. A crossbar switch with SLM is programmable, however, it requires N.sup.2 pixels for the interconnections among N processors, it consumes more energy because of beam splitting, and it is bulky when including lenses.